1. Field of the Invention
The present invention relates generally to video image compression and specifically to a method of compressing and then decompressing either "still" or "moving" video images so that for full-motion, (30 frames per second) and full screen "moving" video transmission on at least a standard 640.times.480 resolution computer display screen in at least 24-bit color depth coding can be transmitted between two computer or video terminals connected either by ordinary telephone wires or other telephone wiring using a 33.6 kilobits per second modem or a 28.8 kilobits per second modem or a 19.6 kilobits per second modem.
2. Description of the Prior Art
In the prior art, several still and moving video image compression and decompression schemes (methods) or algorithms exist. In the case of a 640 pixels on each field line for a total of 480 field lines (640.times.480) resolution display screen of most computers presently in use, these compression and decompression schemes seek to compress the 921, 600 bytes (based on 24-bit color depth coding) of each image frame to a manageable number of bytes or bits suitable for transmission between two computer terminals using either ordinary or other bytes of telephone wires or by satellite means; or for reduced storage disk space. In the special case of transmission between two computer terminals connected by ordinary telephone wires in whole or in part, a modem (modulator-demodulator) circuit is used. Such modems are varied, the most common and most efficient ranging in transmission capacity from around 14,400 bits per second to 28,800 bits per second to 33,600 bits per second and a little beyond.
Unfortunately, with the existing video compression schemes with both hardware/software, hardware only or software only based compression such as MPEG, Indeo, Wavelet, Fractals, etc, the compression ratios though are good ranging from as low as 3 to 1 to well over 100 to 1 over none-compressed video, it is not possible to transmit 30 frames per second (full-motion) in 24-bit color depth coding, full screen video through either a 14,000 bits per second or a 28,000 bits per second or a 33,600 bits per second modem between two computer terminals.
As an example a 100 to 1 compression ratio in 24-bit color depth of an image reduces a 921,600 bytes frame code to 9216 bytes. However, 9216 bytes (73728 bits) cannot be transmitted in one second by a 33.6 kbps modem, without even considering that at that compression ratio 30 image frames would require 2211840 bits to transmit in only one second whereas the modem can transmit only 33600 bits per second. Accordingly, there is a need to provide for a better video image compression scheme to compress a video image to the level where the compressed video image data is small enough to be transmitted between two terminals using available modem circuits.
In U.S. patent application Ser. No. 08/838,324 filed on Apr. 8, 1997 in the names of the present applicant, there is provided a method for compressing a video image using the method of image frame partition to encode the partitioned group of pixels with each such group of pixels that are equal in number being provided a unique binary code based on each colour with average or varying brightness of each pixel within the group. This method provides compression ratios of 20 to 1, 15 to 1, 10 to 1 and 5 to 1 for 32-bit, 24-bit, and 8-bit color depth coding respectively and also 3 to 1 and 1.5 to 1 adjustable compression ratios for 24-bit color depth coding when each pixel is represented by one byte and by two bytes respectively.
All these compression schemes further demonstrate the enormous need to compress video data both for transmission and for storage.